There has been conventionally known a sheet folding apparatus for folding a sheet at a right angle to a sheet feeding direction by nipping the sheet between a pair of folding rollers (also see, for example, Patent Documents 1 and 2). The sheet folding apparatus of this type includes a sheet feeding section for sequentially feeding sheets from a sheet stack and a sheet folding section for folding the sheet fed from the sheet feeding section at a right angle to the sheet feeding direction.
The sheet feeding section includes a rack on which the sheet stack is placed, a conveyor belt extending between the rack and the sheet folding section and rotationally driven, and a sheet feeder for sequentially feeding the sheet from the sheet stack on the rack onto a conveying surface of the conveyor belt.
Furthermore, a guide plate is mounted on the conveyor belt for aligning the sheet to be conveyed. The guide plate extends in the conveyance direction and is movable on the conveyor belt in a direction perpendicular to the conveyance direction. The sheet is conveyed on the conveyor belt in contact with the guide plate at one side edge thereof.
The sheet folding section includes buckles. Each of the buckles has a rectangular outer frame and a plurality of bars which extend between a pair of opposite sides of the outer frame and are spaced each other. Each of the plurality of bars includes a pair of bar elements spaced in a thickness direction of the outer frame. A slot is formed at one of the pair of opposite sides of the outer frame and communicates with a clearance defined between the pair of bar elements of each of the bars. Inside of the buckle is formed a sheet feed clearance extending from the slot into a longitudinal direction of the bar. The buckle is arranged in such a way that the slot is oriented toward the conveyor belt.
A stopper is arranged in the sheet feed clearance of the buckle. When the leading edge of the sheet abuts against the stopper, the sheet is positioned at a predetermined folding position. A pair of inlet rollers is arranged immediately before the slot of the buckle and rotationally driven, so that the sheet fed by the conveyor belt is nipped therebetween, and then fed into the sheet feed clearance of the buckle. A pair of folding rollers is arranged in the proximity of and in parallel to the pair of inlet rollers and rotationally driven so as to fold a portion of the sheet bent outside of the buckle.
In the above-described conventional sheet folding apparatus, a control section receives data of the size of the sheet prior to the start of a sheet folding operation. The control section sets the position of the guide plate of the sheet feeding section based on the data in such a way that the sheet is fed at the center of the buckle of the sheet folding section. Upon the start of the sheet folding operation, the sheets are sequentially delivered between the pair of inlet rollers from the conveyor belt, to be then fed into the buckle. The portion of the sheet bent outside of the buckle is nipped between the pair of folding rollers, and thus, the sheet is folded at the predetermined folding position.
However, in the above-described conventional sheet folding apparatus, occasionally, the sheet may not be accurately folded at the predetermined folding position, so that a deficient product may be produced. It is proved that this failure is not caused by sheet jamming, but the cause of this failure has not been found out heretofore.
Accordingly, in the prior art, an occasional deviation of a sheet folding position is corrected by adjusting parts of a sheet folding apparatus relying on operator's skill and hunch.